1. Field of the Invention
The present invention relates to a 3D woofer drive circuit, and more specifically, to a 3D woofer drive circuit arranged to drive a woofer which is a speaker for a low frequency range in the center of a 3D sound system.
2. Description of the Related Art
FIG. 3 is a circuit diagram illustrating an example of a conventional 3D sound system relating to a background of the present invention. The conventional 3D sound system 1 shown in FIG. 3 includes two input terminals 2a and 2b. 
Two inductors 3a and 3b are connected in series between the two input terminals 2a and 2b. A capacitor 4 is connected between a connection point of the two inductors 3a and 3b and a ground terminal which is a reference potential. A variable resistor 6 is connected to each end of the capacitor 4 and to two speaker terminals 5 for a woofer.
A capacitor 7a and an inductor 8a are connected to each other in series between the input terminal 2a and the ground terminal, and two speaker terminals 9a for an L-channel speaker are connected to each end of the inductor 8a. 
Similarly, a capacitor 7b and an inductor 8b are connected to each other in series between the input terminal 2b and the ground terminal, and two speaker terminals 9b for an R-channel speaker are connected to each end of the inductor 8b. 
In this 3D sound system 1, a woofer is connected to the speaker terminals 5, an L-channel speaker for medium to high frequency range is connected to the speaker terminals 9a, and an R-channel speaker for medium to high frequency range is connected to the speaker terminals 9b. 
In this 3D sound system 1, an L-channel sound signal is input between the input terminal 2a and the ground terminal, while an R-channel sound signal is input between the input terminal 2b and the ground terminal. Thus, the low frequency range sound signal among the sound signals in which the L-channel sound signal is synthesized with the R-channel sound signal is converted into sound by the woofer, the medium to high frequency range sound signal in the L-channel sound signal is converted into sound by the medium to high frequency range L-channel speaker, and the medium to high frequency range sound signal in the R-channel sound signal is converted into sound by the medium to high frequency range R-channel speaker.
FIG. 4 is a circuit diagram illustrating another example of a conventional 3D sound system relating to the background of the present invention. A conventional 3D sound system 11 illustrated in FIG. 4 includes a pre-amplifier 12. The pre-amplifier 12 is provided with two input terminals 13a and 13b and two output terminals 14a and 14b. 
Two resistors 15a and 15b are connected in series between the two output terminals 14a and 14b of the pre-amplifier 12. A capacitor 16 is connected between the connection point of the two resistors 15a and 15b and the ground terminal which is the reference potential. Two speaker terminals 18 for the woofer are connected to each end of the capacitor 16 through a main amplifier 17.
A capacitor 19a and a resistor 20a are connected in series between the output. terminal 14a of the pre-amplifier 12 and the ground terminal, and two speaker terminals 22a for the L-channel speaker are connected to each end of the resistor 20a through a main amplifier 21a. 
Similarly, a capacitor 19b and a resistor 20b are connected in series between the output terminal 14b of the pre-amplifier 12 and the ground terminal, and two speaker terminals 22b for the R-channel speaker are connected to each end of the resistor 20b through a main amplifier 21b. 
In the 3D sound system 11, the woofer is connected to the speaker terminals 18, the medium to high frequency range L-channel speaker is connected to the speaker terminals 22a, and the medium to high frequency range R-channel speaker is connected to the speaker terminals 22b. 
In the 3D sound system 11, the L-channel sound signal is input between the input terminal 13a of the pre-amplifier 12 and the ground terminal, and the sound signal of the R-channel is input between the input terminal 13b of the pre-amplifier 12 and the ground terminal. The low frequency range sound signal among the sound signals in which the L-channel sound signal is synthesized with the R-channel sound signal is converted into sound by the woofer, the medium to high frequency range sound signal in the L-channel sound signal is converted into sound by the medium to high frequency range L-channel speaker, and the medium to high frequency range sound signal in the R-channel sound signals is converted into sound by the medium to high frequency range R-channel speaker.
In the 3D sound system 1 illustrated in FIG. 3, the impedance of the woofer forming a load is low, and the values of the inductance and the capacitance of the inductors 3a and 3b, and the capacitor 4 constituting a network for the woofer are increased, the size is increased, and the power must also be considered.
Further, in the 3D sound system 1 illustrated in FIG. 3, the variable resistor 6 to regulate the level of the woofer must be impedance-matched with the woofer forming the load, and a specialized variable resistor must be used, its size is large, its cost is high, and the power must also be considered.
In addition, in the 3D sound system 1 illustrated in FIG. 3, if the tone of the woofer is to be adjusted, the tone must be adjusted at the woofer itself.
In the 3D sound system 11 illustrated in FIG. 4, a plurality of amplifiers including the pre-amplifier and the main amplifier are required to drive the woofer.
Also, in the 3D sound system 11 illustrated in FIG. 4, the construction of the driver for the woofer becomes complicated, and the whole system is increased in size and cost.
Accordingly, in order to overcome the problems described above, preferred embodiments of the present invention provide a 3D woofer drive circuit which miniaturizes a 3D sound system and greatly reduces the cost thereof.
A 3D woofer drive circuit according to preferred embodiments of the present invention for driving the woofer in the center of a 3D sound system includes an impedance element arranged to synthesize an L-channel sound signal with an R-channel sound signal and an amplifier arranged to output to the woofer the sound signal synthesized by the impedance element for driving the woofer.
In the 3D woofer drive circuit of preferred embodiments of the present invention, the impedance element includes a resistor, a capacitor connected to the resistor, and a low pass filter arranged to control the frequency of the sound signal to be output to the woofer by the resistor and the capacitor may be provided. In this case, a variable resistor which also has the function of an attenuator and a tone control may be used as the resistor to be used in the low pass filter.
In the 3D woofer drive circuit of preferred embodiments of the present invention, the L-channel sound signal is synthesized with the R-channel sound signal via the impedance element, the synthesized sound signal is output to the woofer by the amplifier, thus driving the woofer, and the sound signal is converted into sound by the woofer.
In preferred embodiments of the present invention, it is not necessary that the network for the woofer include the inductor and the capacitor, and a plurality of amplifiers to drive the woofer can be eliminated, and the constitution of the 3D woofer drive circuit is thereby greatly simplified. Thus, the 3D sound system is miniaturized and the cost is reduced if the 3D woofer drive circuit of preferred embodiments of the present invention is used in the 3D sound system.
The above-mentioned elements, features, characteristics and advantages of the present invention are further clarified by the following detailed description of preferred embodiments referring to the drawings.